Inert gas flooding fire suppression with water augmentation

ABSTRACT

A method and system are provided for suppressing a fire inside a defined volume within a structure. To suppress a fire, the defined volume is flooded with a flow of inert gas into which a limited amount of water is introduced into the flow of inert gas; the flow of inert gas and the limited amount of water introduced therein being sufficient to establish a fire extinguishing atmosphere within the defined volume having a volumetric oxygen concentration of at least about 14%. A cartridge for storing a limited amount of water has a water outlet in flow communication with a spray nozzle that is in flow communication with a supply of pressurized inert gas. The water storage cartridge has a gas inlet in flow communication with a supply of pressurized inert gas for pressurizing the water storage cartridge to cause water to flow therefrom to the spray nozzle.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to International Patent Application SerialNo. PCT/US07/(Attorney Docket No. 1463_(—)002), entitled “HYBRID INERTGAS FIRE SUPPRESSION SYSTEM”, filed with the United States Patent andTrademark Office on the same date as this application and subject toassignment to the common assignee of this application.

FIELD OF THE INVENTION

This invention relates generally to fire suppression systems. Moreparticularly, this invention relates to a fire suppression systemproviding inert gas flooding fire suppression with water augmentation.

BACKGROUND OF THE INVENTION

Fire suppression fire systems are often installed in commercialbuildings. Typically, those buildings are subdivided into multiplerooms. Commonly, conventional fire suppression systems are designedeither as total flooding systems using an inert gas under pressure orlocalized streaming fire suppression systems using liquid suppressantunder pressure. In total flooding systems, an inert gas is rapidlyadmitted into a room, commonly through a plurality of nozzles mounted inan array in the ceiling of the room, to fill the volume defined withinthe room. The inert gas may be nitrogen, carbon dioxide, argon, neon,helium or other chemically non-reactive gas, or mixtures of any two ormore of these gases. For example, a mixture of 50% argon and 50%nitrogen is commonly used in inert gas fire suppression system. Theinert gas not only removes heat from the fire, but also dilutes theoxygen content within the room to a level low enough that combustion cannot be sustained. Typically, conventional inert gas systems are sized toreduce the oxygen content in the atmosphere within the environment ofthe protected area to a level below 12.5 percent within one minute.Consequently, a large number of high-pressure cylinders of inert gas,typically at a pressure between 200 to 300 bars must be provided tostore the necessary volume of inert gas. A large centralized storagearea must be dedicated for placement of the required inert gas storagecylinders.

Conventional streaming fire suppression systems spray a mist of liquidsuppressant over a localized area beneath the spray cone of adistribution nozzle. Commonly, a number of distribution spray nozzlesare arrayed over the space being protected and are supplied with liquidsuppressant, for example water or a liquid chemical agent, from acentralized source. Typically, the liquid suppressant is fed underpressure and conveyed through a network of pipes to the variousindividual distribution nozzles. Generally, the distribution nozzles aredesigned to emit a mist of liquid suppressant having a droplet size inthe range of between 5 and 60 micrometers. The mist may be producedsimply by forcing the liquid suppressant through the openings of thenozzle or through atomization means incorporated in the nozzle.

U.S. Patent Application Publication No. US2005/073131A1 discloses a fireand explosion suppression system wherein high pressure water from acentral storage tank is suspended in a flow of nitrogen gas or a mixtureof nitrogen and argon gases and distributed to an array of a pluralityof distribution nozzles and emitted as a mist of water droplets over alocalized area. U.S. Patent Application Publication No. 2006/0278410discloses a fire and explosion system wherein high pressure water from acentral storage tank is passed through a network of pipes to a pluralityof high velocity low pressure emitters wherein the water is atomized anddischarged into a high pressure inert gas stream passing out of theemitter. U.S. Pat. No. 7,153,446, also published as Patent ApplicationPublication No. US2005/0144949A1, discloses a fire and explosionsuppression system wherein a liquid chemical agent fire suppressantunder pressure from a central storage tank is suspended in a flow ofinert gas and is distributed to an array of a plurality of distributionnozzles and emitted as a mist of liquid droplets over a localized area.A number of exemplary liquid chemical agents suitable for use as firesuppressants are also disclosed in U.S. Pat. No. 7,153,446.

A form of fire suppression system using a commercially available liquidchemical fire suppressant is commonly referred to as a clean agentgaseous fire suppression system because the chemical agent leaves noresidue upon evaporation. Clean agent fire suppression systems are ofteninstalled in rooms or areas of buildings wherein equipment or goods arehoused that could be damaged by water, powder or foam. In a system ofthis type, a chemical fire suppression agent that is stored in a tank orcylinder as a liquid under pressure is pushed by a gaseous propellant,typically nitrogen, argon or carbon dioxide, from a tank or cylinder ofpropellant arranged in series flow relationship with the tank orcylinder of chemical agent, through a network of pipes to and through aplurality of distribution nozzles arrayed across the ceiling area orwalls of the space being protected. The chemical fire suppression agentis a volatile chemical that exists as a liquid when confined underpressure in a closed vessel, but rapidly vaporizes from its liquid stateto a vapor state when sprayed via the distribution nozzles into theambient atmosphere to form a gaseous mixture with the air within thespace being protected which does not support combustion and extinguishesfires. The distribution nozzles function to atomize or otherwise breakthe liquid chemical fire suppressant into small droplets to facilitateevaporation. An example of a clean agent gaseous fire suppression systemis disclosed in each of U.S. Pat. No. 6,763,894 and U.S. PatentApplication Publication No. US2005/0001065A1.

SUMMARY OF THE INVENTION

In an aspect of the invention, a method is provided for suppressing afire inside a defined volume within a structure, including the steps offlooding the defined volume with a flow of inert gas, and introducing alimited amount of water into the flow of inert gas. The flow of inertgas introduced into the defined volume and the limited amount of waterintroduced therein are sufficient to establish a fire extinguishingatmosphere within the defined volume having a volumetric oxygenconcentration of at least about 14%. The amount of water introduced intothe flow of inert gas may be limited to a volumetric ratio of the volumeof water to the volume of inert gas in the range of about 0.02% to0.05%. The step of flooding the defined volume with a flow of inert gasmay comprise the step of flooding the defined volume with a flow ofchemically non-reactive gas selected from the group including nitrogengas, carbon dioxide gas, helium gas, argon gas, neon gas, and mixturesof two or more thereof.

In an aspect of the invention, a method is provided for suppressing afire inside a defined volume within a structure, including the steps of:storing a supply of inert gas under pressure, providing at least oneinert gas spray nozzle within the defined volume, storing a supply ofwater in a reservoir in the vicinity of the at least one inert gas spraynozzle, detecting a fire within the defined volume, flooding the definedvolume with pressurized inert gas by passing a flow of pressurized inertgas from the supply of inert gas through the at least one inert gasnozzle, and pressurizing the water reservoir with a flow of pressurizedinert gas from the supply of inert gas to force a flow of water from thewater reservoir into the flow of pressurized inert gas. In anembodiment, the method further includes the step of introducing waterfrom the water reservoir directly into the inert gas flow upstream ofthe spray nozzle. In an embodiment, the method further includes the stepof introducing water from the water reservoir into the inert gas flowpassing from the spray nozzle.

In another aspect of the invention, a fire suppression system isprovided for establishing a fire extinguishing atmosphere within adefined volume in response to detection of a fire within the definedvolume. The fire suppression system includes at least one inert gasspray nozzle assembly for introducing a flooding flow of inert gas intothe defined volume and a water storage cartridge defining a reservoirfor storing a limited amount of water. The inert gas spray nozzleassembly includes a spray nozzle that is disposed within the definedvolume and connected in flow communication with a supply of pressurizedinert gas. The water storage cartridge is disposed in close proximity tothe spray nozzle and has a pressurizing gas inlet in flow communicationwith the supply of pressurized inert gas and a water outlet in flowcommunication with said spray nozzle.

In an embodiment, the water storage cartridge has an elongated bodyextending along a longitudinal axis between an aft end and a forward endand having an interior volume defining the water reservoir. The forwardend of said body may be disposed adjacent the spray nozzle. A gas flowconduit establishes flow communication between the supply of pressurizedinert gas and the interior volume of the water storage cartridge throughan outlet opening to the interior volume of the water storage cartridgethrough an upper portion of the aft end of the water storage cartridge.A water conduit establishes flow communication between the interiorvolume of the water storage cartridge and the spray nozzle through aninlet opening to the interior volume of the water storage cartridgethrough a lower portion of the forward end of the water storagecartridge. In an embodiment, the water conduit has an outlet openinginto an interior cavity of the spray nozzle. A flow restriction orificemay be disposed in the water conduit. In an embodiment, a gas flowrestriction orifice may be disposed in the inert gas supply line betweenthe gas conduit opening thereto and the water conduit opening thereto.

In an embodiment of the fire suppression system, an inert gas supplypipe in flow communication with the supply of pressurized inert gas hasa terminus to which the spray nozzle is mounted and a water conduitestablishes flow communication between the interior volume of the waterstorage cartridge and the spray nozzle. The water conduit has an inletopening to the interior volume of the water storage cartridge through alower portion of the forward end of the water storage cartridge and anoutlet opening into a terminal portion the inert gas supply pipeupstream with respect to inert gas flow therethrough of the spraynozzle. A gas flow conduit establishes flow communication between thesupply of pressurized inert gas and the interior volume of the waterstorage cartridge through an inlet opening to an upstream portion of theterminal portion of the inert gas supply pipe and an outlet opening tothe interior volume of the water storage cartridge through an upperportion of the aft end of the water storage cartridge. A flowrestriction orifice may be disposed in the terminal portion of the inertgas supply pipe downstream with respect to inert gas flow of the inletof the gas conduit to the terminal portion of the inert gas supply lineand upstream with respect to inert gas flow of the outlet of the waterconduit to the terminal portion of the inert gas supply pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of these and other objects of the invention,reference will be made to the following detailed description of theinvention which is to be read in connection with the accompanyingdrawing, where:

FIG. 1 is a depiction, partly is schematic and partly in perspective, ofan exemplary embodiment of a fire suppression system in accord with theinvention;

FIG. 2 is a sectioned side elevation view of the first embodiment of thenozzle assembly depicted in FIG. 1;

FIG. 3 is a sectioned elevation view of the spray nozzle shown in FIG.2;

FIG. 4 is a sectioned side elevation view of the second embodiment ofthe nozzle assembly depicted in FIG. 1;

FIG. 5 is a sectioned elevation view of the spray nozzle shown in FIG.4;

FIG. 6 is a bar graph illustrating the oxygen content of a fireextinguishing atmosphere for the hybrid inert gas fire suppressionsystem of the invention in comparison to conventional Nitrogen andArgon/Nitrogen inert gas fire suppression systems; and

FIGS. 7A, 7B and 7C are schematic illustrations of three respectiveexemplary embodiments depicting alternate locations of the water storagecartridge relative to the inert gas distribution network of the hybridinert gas fire suppression system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-5 in particular, there is depicted an exemplaryembodiment of a hybrid inert gas fire suppression system 10 with wateraugmentation in accord with the invention. The system 10 includes one ormore vessels 12 for storing an inert gas, i.e. a chemically non-reactivegas, such as nitrogen, argon, neon, helium, carbon dioxide or a mixtureof two or more of these gases, and at least one spray nozzle assembly20. Although two spray nozzle assemblies 20 are depicted in theexemplary embodiment of the system 10 illustrated in FIG. 1, it will beunderstood by those skilled in the art that the actual number of spraynozzle assemblies installed in any particular application will dependupon the volume and planar area of the protected space.

The inert gas storage vessels 12, each of which contains inert gas underpressure, typically at a pressure of 200 to 300 bars, are connected inflow communication with the spray nozzle assemblies 20 via a network ofpipes 15, 15A and 15B. The pipes 15A and 15B, each of which branches offthe main inert gas supply pipe 15 to feed inert gas to a respective oneof the spray nozzle assemblies 20, may be referred to as a distributionpipe. As in conventional inert gas fire suppression systems, a pressureregulator 14 is disposed at the outlet of each of the inert gas vessels12 for regulating the pressure leaving the inert gas vessels 12 tomaintain an initial desired gas pressure within the inert gas flow line,typically up to 150 bars. A gas flow regulator 16 is disposed in pipe 15downstream of the pressure regulator 14 for controlling the flow ofinert gas through the pipe 15. Alternatively, the gas pressure regulator14 and the gas flow regulator 16 may be collocated or even combined intoa single valve or flow control device. A sensor 70 may be installedwithin the protected space 100 for detecting the existence of a firewithin the protected space and for generating a fire detected signal.When a fire is detected, a fire detected signal 71 is transmitted fromthe sensor 70 to the system controller 18 which, in response to receiptof the fire detected signal 71, generates the demand signal 17 andtransmits the demand signal 17 to the gas flow regulator 16 which, inresponse to receipt of the demand signal 17, opens to allow pressurizedinert gas from the vessels 12 to flow through the pipes 15, 15A and 15Bto the respective spray nozzle assemblies 20.

Each of the spray nozzle assemblies 20 includes a spray nozzle 30A or30B mounted to the terminus of the terminal section of a respective oneof the distribution pipes 15A and 15B that branch off of the inert gassupply pipe 15. The spray nozzle assemblies 20 are disposed above theceiling 102 of the protected space 100 in the open space 105 that existsabove the ceiling 102 and beneath the floor 104 of the next storythereabove or the roof of the structure, commonly referred to as theceiling void. As in conventional practice, the terminal section of eachof the branch pipes 15A and 15B extends generally vertically downwardsuch that the spray nozzles 30A or 30B are disposed subadjacent theroom-side, i.e. lower side, surface of the ceiling 102 extending overthe protected space 100.

Each of the spray nozzle assemblies 20 of the hybrid inert gas floodingfire suppression system 10 of the invention further includes a reservoirof water 50 disposed in the ceiling void 105 in operative associationwith its respective one of the spray nozzles 30A and 30B. The reservoirof water 50 is stored at atmospheric pressure within the interior volume55 of an elongated cartridge 52 having an aft end 54 and a forward end56. As depicted in the exemplary embodiments shown in FIGS. 2 and 4, thewater storage cartridge may be a cylinder. However, it is to beunderstood that the water storage cartridge could be in the form of asphere, a rectangular parallelepiped, or any other suitable form. In theexemplary embodiments depicted in FIGS. 2 and 4, the cartridge 52 isdisposed in association with the terminal section of each of therespective branch pipes 15A and 15B with the forward end 56 of the waterstorage cartridge 52 disposed in neighboring relationship with the spraynozzle 30A, 30B of the spray nozzle assembly 20. However, as will bediscussed in further detail hereinafter, the water storage cartridges 52may alternatively be located further upstream on the respective branchpipes 15A and 15B, that is more remote from the respective spray nozzles30A and 30B rather than being located in association with the terminalsection of the branch pipes 15A and 15B.

In the exemplary embodiment depicted in FIGS. 2 and 3, the spray nozzle30A is a dual fluid atomizer having a body 34 defining an upper cavity33 and a lower cavity 35. Water from the reservoir 50 passing throughconduit 53 is introduced directly into the upper cavity 33 and inert gasis introduced directly into the lower cavity 35. A plurality of openings37 through the lower side wall of the nozzle body 34 provide a pluralityof circumferentially spaced outlets through which inert gas passes fromthe lower cavity 35. The inert gas enters the lower cavity 35 travelinggenerally vertically downward and turns to follow along the floor of thelower cavity and exit generally horizontally in the protected space 100through the openings 37. Water exits from the upper cavity 33 generallyvertically downward into the protected space through a plurality ofopenings 36 extending through the floor of the upper cavity atcircumferentially spaced intervals located radially outward of the lowerside wall of the nozzle body. As the water passes generally verticallydownward, it is impacted by the generally horizontally directed inertgas causing the water to be atomized into a droplet mist and entrainedin the inert gas stream to penetrate together with the inert gas intothe ambient atmosphere within the protected space 100. It is to beunderstood that the dual fluid atomizer described herein is merelyexemplary and that various other configurations of dual fluid atomizersmay be used in connection with the fire suppression system and method ofthe invention.

In the exemplary embodiment depicted in FIGS. 4 and 5, since the waterfrom the reservoir 50 passing through conduit 51 is introduced into andmixes with the inert gas flow passing through the terminal portion ofthe distribution pipe 15B upstream of the spray nozzle 30B, the spraynozzle 30B may comprise any conventional distribution-type spray nozzle.For example, the spray nozzle 30B may have a plurality of openings 31,which in the depicted embodiment are arrayed in one or more rows atcircumferentially spaced intervals about the body 32 of the spraynozzle. However, it is to be understood, that the openings 31, which maybe holes or elongated slots or other shaped apertures, may be arrayed orotherwise disposed in other arrangements. In this type of spray nozzle,atomization of the water entrained in the inert gas flow occurs as aresult of the force of the pressure drop encountered as the water/inertgas mix passes through the openings 31 and penetrates into the ambientatmosphere within the protected space 100.

A water conduit 51 establishes water flow communication between theinterior volume 55 of the water storage cartridge 52 through an outlet53 at the lower portion of the forward end 56 of the cartridge 52 andthe respective spray nozzle 30A, 30B associated with the cartridge 52.In the exemplary embodiment depicted in FIGS. 2 and 3, the water conduit51 opens into the upper cavity of the spray nozzle 30A. In the exemplaryembodiment depicted in FIGS. 4 and 5, the conduit 51 opens into theterminal portion of the distribution pipe 15B upstream of the spraynozzle 30B and on the upper side of the ceiling 102. A check valve 58 isdisposed in the conduit 51 downstream of the outlet 53 from the waterstorage cartridge 52 to prevent back flow through the conduit 51.

A gas conduit 57 establishes inert gas flow communication between theinert gas distribution line 15A, 15B associated with the water storagecartridge 52 and the interior volume 55 of the cartridge 52 through aninlet 59 at the upper portion of the aft end 54 of the cartridge 52. Aback flow prevention means 28, such as a check valve or burst diaphragm,may be disposed in the gas conduit 57 to prevent back flow of watertherethrough into gas conduit 57 when the inert gas distribution lines15A, 15 b are not pressurized, that is when inert gas is not flowingtherethrough. As depicted in the exemplary embodiment illustrated inFIG. 4, a flow restriction orifice 25 may be inserted in thedistribution pipe 15B at a location downstream of the opening of the gasconduit to the distribution pipe 15B and upstream of the opening of thewater conduit 53 to the terminal portion of the distribution pipe 15Bfor the purpose of increasing the pressure drop experienced by the inertgas flowing therethrough thereby further increasing the pressuredifferential between the pressure of the inert gas admitted to thereservoir 55 within the water storage cylinder 50 and the gas pressureat the downstream location at which the water is emitted from the waterstorage cartridge 50 into distribution pipe 15B.

As noted previously, when a fire is detected within the protected space100, the controller 18 sends a demand signal 17 to the flow controlvalve 16 causing the flow control valve 16 to open, thereby allowingpressurized inert gas to flow from the inert gas storage vessels 12 at acontrolled rate through the main supply pipe 15 to and through thedistribution pipes 15A and 15B and into the protected space 100 throughthe spray nozzles 30A and 30B. Additionally, a portion of the inert gaspassing through the distribution pipes 15A and 15B passes through therespective gas conduit 57 associated with each spray nozzle assembly 20to pressure the interior volume 55 of the water storage cartridge 52thereby forcing water to flow from the water reservoir 50 through waterconduit 51 to be introduced into the inert gas as hereinbeforedescribed. As the inert gas is introduced into the interior volume 55 ofthe water storage cartridge at a gas pressure substantially higher thanthe gas pressure at the location at which the water is introduced intothe inert gas flow, the water within the reservoir 50 will rapidly flowtherefrom.

A rapid flow rate of water is desired in order to empty the water fromthe reservoir 50 within a relatively short period of time, typically oneminute or less. To provide a relatively constant flow rate over theshort period of time in which the reservoir 50 is to be emptied, a waterflow orifice assembly 60 may be disposed in the water conduit 51downstream of the outlet 53 from the water storage cartridge 52. Theorifice is sized appropriately to provide a desired pressure dropsufficient to affect a relatively constant mass flow ratio of water massflow rate through the water conduit 51 to the inert gas mass flow rate.Due to the high pressure of the inert gas emitted into the interiorvolume within the water storage cartridge 52, without the orificepresent to provide this pressure drop, the water flow through the waterconduit 51 will decay over the time period required to empty thereservoir 50 from a relatively high flow rate initially to a relativelylow rate near the end of the time period.

In conventional inert gas flooding fire suppression systems, the inertgas not only raises the heat capacity of the atmosphere in the protectedspace into which the inert gas is introduced, but also reduces thevolumetric concentration of oxygen in the atmosphere within theprotected space to a level less than 14%, which is generally accepted asa volumetric oxygen concentration that gives personnel within theprotected space an adequate opportunity to evacuate the premises. Incombination, the increase in heat capacity and reduction in oxygenconcentration establishes a fire extinguishing atmosphere within theprotected space. Thus, in buildings or other installations equipped withconventional inert gas systems that operate to totally flood theprotected space with a fire extinguishing atmosphere, personnel withinthe protected space at the time of activation of the fire suppressionsystem can safely remain within the protected space for only a shortperiod of time and therefore must rapidly evacuate the protected space.

Applicants have found that the admission of a limited amount of waterinto the inert gas flooding flow results in a hybrid inert gas firesuppression system that not only floods the protected space with aneffective fire extinguishing atmosphere, but also provides a saferatmosphere for humans and animals within the protected space. Referringnow to FIG. 6, a bar graph is presented that compares the volumetricoxygen concentration characteristically present in the resultant fireextinguishing atmosphere produced when rooms of various volumes areflooded via inert gas from a conventional pure inert gas firesuppression system employing a mixture of equal parts of a nitrogen gasand argon gas, represented by bars A, a conventional pure inert gas firesuppression system employing a nitrogen gas, represented by bars B, anda hybrid inert gas fire suppression system that employs nitrogen gaswith water augmentation in accord with the present invention,represented by bars C. As illustrated, the volumetric oxygenconcentrations in the fire extinguishing atmosphere produced via theconventional inert gas fire suppression systems, represented by bars Aand B, range from slightly less than 9% to about 12.5%.

However, the volumetric oxygen concentrations in the fire extinguishingatmosphere produced via the hybrid inert gas fire suppression system ofthe invention, represented by bars C, range from about 13% to about14.5%. Further, for each defined volume, the volumetric oxygenconcentration of the fire extinguishing atmosphere produced via thehybrid inert gas fire suppression system of the invention was about 2%higher than the volumetric oxygen concentration characteristic of aconventional pure nitrogen gas fire suppression system (bars B), andabout 4% higher than the volumetric oxygen concentration characteristicof a conventional argon/nitrogen gas fire suppression system (bars A).With a higher volumetric oxygen concentration in the resultant fireextinguishing atmosphere, the hybrid inert gas fire suppression systemof the invention is safer for humans and animals present in theprotected space at the time of activation of the fire suppressionsystem. The higher volumetric oxygen concentration within the resultantfire extinguishing atmosphere improves the conditions and lengthens thetime conducive for emergency evacuation, thereby providing personnelwithin the protected space a better opportunity to safely evacuate thepremises.

The added water augments the fire suppression capability of the inertgas by increasing the heat capacity of the resultant fire extinguishingatmosphere as compared to pure inert gas systems. This increase in heatcapacity compensates for the lesser reduction in the volumetric oxygenconcentration. Thus, the hybrid inert gas fire suppression system of theinvention is capable of providing an effective flooding fireextinguishing atmosphere while providing a safer atmosphere forpersonnel occupying the protected space at the time of activation of thefire suppression system. Additionally, the amount of inert gas requiredin operation of the hybrid inert gas fire suppression system of theinvention is reduced relative to the amount required in a similarlysized conventional inert gas system because the heat capacity of thefire extinguishing atmosphere has been augmented by the water introducedinto the inert gas flow. As a result, the amount of inert gas that mustbe stored for use in connection with an installed inert gas system canbe reduced with the hybrid fire suppression system of the invention.

In the hybrid fire suppression system of the invention, the amount ofwater introduced into the inert gas should be limited. If an excessiveamount of water is introduced into the inert gas, the inert gas floodingeffect would be lost and the system would operate similar toconventional water streaming fire suppression systems. The amount ofwater introduced into the flow of inert gas should also be limited toensure that all of the water is rapidly evaporated upon introductioninto the protected space. For example, with the hybrid inert gas firesuppression system of the invention installed in a building for firesuppression within a room having a volume of about 100 cubic meters, tosuppress a fire therein, between 4 and 15 liters of water would beintroduced into a mass flow of about 30 kilograms of inert gasintroduced into the room through a single spray nozzle.

Referring now to FIGS. 7A, 7B and 7C, as noted previously, the waterstorage reservoir 50 may be located at various locations relative to theinert gas branch pipes and the spray nozzles. In an embodiment, asillustrated in FIG. 7A, the water storage reservoir 50 is disposed inassociation with the terminal portion of the inert gas branch pipe 15B.In this embodiment, which also reflects the embodiment shown in FIG. 4,the inert gas supply conduit 57 taps into the terminal portion of theinert gas branch line 15B upstream of the water conduit 51 that opensinto the terminal portion of the branch line 15B near the terminusthereof to which the spray nozzle 30B is mounted. In the embodimentillustrated in FIG. 7B, however, the water storage reservoir 50 isdisposed in association with an upstream portion of the inert gas branchpipe 15B. In this embodiment, the inert gas supply conduit 57 taps intothe inert gas branch line 15B upstream of the water conduit 51 thatopens into an upstream portion of the branch line 15B, rather than intothe downstream terminal portion of the branch line 15B. In theembodiment illustrated in FIG. 7C, the water conduit 51 opens into anupstream portion of the branch line 15B, rather than into the downstreamterminal portion of the branch line 15B, and the inert gas supplyconduit 57 taps into the inert gas distribution line 15 upstream of thepoint at which the branch line 15B taps into the inert gas distributionline 15. In each of these embodiments, a gas flow restriction orifice 25may be disposed in the branch line 15B intermediate the point at whichthe gas conduit 57 connects and the point at which the water conduit 51opens into the branch line 15B to impart pressure drop to the to inertgas flow thereby increasing the pressure differential between thelocation at which the inert gas is drawn off and the location at whichthe water is admitted to the inert gas flow.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawing, itwill be understood by one skilled in the art that various changes indetail may be effected therein without departing from the spirit andscope of the invention as defined by the claims.

1. A method of suppressing a fire inside a defined volume within astructure, comprising the steps of: flooding the defined volume with aflow of inert gas; and introducing a limited amount of water into theflow of inert gas, the flow of inert gas and the limited amount of waterintroduced therein being sufficient to establish a fire extinguishingatmosphere within the defined volume having a volumetric oxygenconcentration of at least about 14%.
 2. A method of suppressing a fireas recited in claim 1 further comprising the step of limiting the amountof water introduced into to the flow of inert gas to a mass flow ratioof the mass flow of water to the mass flow of inert gas in the range ofabout 0.02% to about 0.05%.
 3. A method of suppressing a fire as recitedin claim 1 wherein the step of flooding the defined volume with a flowof inert gas comprises the step of flooding the defined volume with aflow of chemically non-reactive gas selected from the group includingnitrogen gas, carbon dioxide gas, helium gas, argon gas, neon gas, andmixtures of two or more thereof.
 4. A method of suppressing a fireinside a defined volume within a structure, comprising the steps of:storing a supply of inert gas under pressure; providing at least oneinert gas spray nozzle within the defined volume; storing a supply ofwater in a reservoir in the vicinity of said at least one inert gasspray nozzle; detecting a fire within the defined volume; flooding thedefined volume with pressurized inert gas by passing a flow ofpressurized inert gas from said supply of inert gas through said atleast one inert gas spray nozzle; and pressurizing the water reservoirwith a flow of pressurized inert from said supply of inert gas to forcea flow of water from the water reservoir into the flow of pressurizedinert gas.
 5. A method of suppressing a fire as recited in claim 4wherein the flow of inert gas and the limited amount of water introducedtherein being sufficient to establish a fire extinguishing atmospherewithin the defined volume having a volumetric oxygen concentration of atleast about 14%.
 6. A method of suppressing a fire as recited in claim 4comprising the further step of introducing water from the waterreservoir directly into the inert gas flow upstream of the spray nozzle.7. A method of suppressing a fire as recited in claim 4 comprising thefurther step of introducing water from the water reservoir into theinert gas flow passing from the spray nozzle.
 8. A method of suppressinga fire as recited in claim 7 wherein the flow of inert gas and thelimited amount of water introduced therein being sufficient to establisha fire extinguishing atmosphere within the defined volume having avolumetric oxygen concentration of at least about 14%.
 9. A method ofsuppressing a fire as recited in claim 4 further comprising the step oflimiting the amount of water introduced into to the flow of inert gas toa mass flow ratio of the mass flow of water to the mass flow of inertgas in the range of about 0.02% to about 0.05%.
 10. A method ofsuppressing a fire as recited in claim 4 wherein the step of floodingthe defined volume with a flow of inert gas comprises the step offlooding the defined volume with a flow of chemically non-reactive gasselected from the group including nitrogen gas, carbon dioxide gas,helium gas, argon gas, neon gas, and mixtures of two or more thereof.11. A fire suppression system for establishing a fire extinguishingatmosphere within a defined volume in response to detection of a firewithin the defined volume, comprising: at least one inert gas spraynozzle assembly for introducing a flooding flow of inert gas into thedefined volume, said at least one inert gas spray nozzle assemblyincluding a spray nozzle disposed within the defined volume and a waterstorage cartridge defining a reservoir for storing a limited amount ofwater in proximity to said spray nozzle, said spray nozzle in flowcommunication with a supply of pressurized inert gas, said water storagecartridge having a pressurizing gas inlet in flow communication with thesupply of pressurized inert gas and a water outlet in flow communicationwith said spray nozzle.
 12. A fire suppression system as recited inclaim 11 wherein said water storage cartridge comprises an elongatedbody extending along a longitudinal axis between an aft end and aforward end and having an interior volume defining said water reservoir;the forward end of said body being disposed adjacent said spray nozzle.13. A fire suppression system as recited in claim 12 further comprisinga gas flow conduit establishing flow communication between the supply ofpressurized inert gas and the interior volume of said water storagecartridge, the gas conduit having an outlet opening to the interiorvolume of said water storage cartridge through an upper portion of theaft end of said water storage cartridge.
 14. A fire suppression systemas recited in claim 12 further comprising a water conduit establishingflow communication between the interior volume of said water storagecartridge and said spray nozzle, the water conduit having an inletopening to the interior volume of said water storage cartridge through alower portion of the forward end of said water storage cartridge.
 15. Afire suppression system as recited in claim 14 wherein said waterconduit has an outlet opening into an interior cavity of said spraynozzle.
 16. A fire suppression system as recited in claim 14 furthercomprising a flow restriction orifice disposed in said water conduit.17. A fire suppression system as recited in claim 11 further comprising:an inert gas supply pipe in flow communication the supply of pressurizedinert gas, the inert gas supply pipe having a terminal portion having aterminus, said spray nozzle mounted to the terminus of the inert gassupply pipe.
 18. A fire suppression system as recited in claim 17further comprising: a water conduit establishing flow communicationbetween the interior volume of said water storage cartridge and saidspray nozzle, the water conduit having an inlet opening to the interiorvolume of said water storage cartridge and an outlet opening into theterminal portion the inert gas supply pipe upstream with respect toinert gas flow therethrough of said spray nozzle.
 19. A fire suppressionsystem as recited in claim 18 further comprising a gas flow conduitestablishing flow communication between the supply of pressurized inertgas and the interior volume of said water storage cartridge, the gasconduit having an inlet opening to an upstream portion of the terminalportion of the inert gas supply pipe and an outlet opening to theinterior volume of said water storage cartridge through an upper portionof the aft end of said water storage cartridge
 20. A fire suppressionsystem as recited in claim 19 further comprising a flow restrictionorifice disposed in the terminal portion of the inert gas supply pipedownstream with respect to inert gas flow of the inlet of the gasconduit to the terminal portion of the inert gas supply line andupstream with respect to inert gas flow of the outlet of the waterconduit to the terminal portion of the inert gas supply pipe.